The present invention is related to a rolling bearing unit with a rotational speed sensor, which is utilized to rotatably support a road wheel with reference to a suspension apparatus while detecting the rotational speed of the road wheel.
The road wheel is rotatably supported by a rolling bearing unit with reference to a suspension apparatus. In addition, the rotational speed of the road wheel must be detected in order to control an anti-lock braking system (ABS) and traction control system (TCS). Accordingly, recently the rolling bearing unit with rotational speed sensor, that is the rolling bearing unit having a rotational speed sensor installed therein, is broadly used to rotatable support the road wheel while detecting the rotational speed of the road wheel.
Japanese Utility Model Publication JITSUKAI HEI No. 7-31539 discloses one example of the prior art structures of the rotational speed sensor, which is also referred to as rpm detector in this specification, for use in such an object.
An object of this publication is to provide a rolling bearing unit with rotation speed sensor wherein it is possible to take out only the rotation speed sensor from the hub cap for exchange and maintenance, to make short the axial size of the bearing unit, and to stabilize the sensor performance.
In this structure, a pair of bolts and nuts are used to securely fix a sensor to a cover of the rolling bearing unit. (see e.g. FIG. 3 of the publication). This step is carried out in the assembling site of the rolling bearing unit with rotational speed sensor but inconvenient to need a long process time. In addition, the disengagement and engagement of the bolts and nuts for repairing the rotational speed sensor in the rolling bearing unit are also troublesome. This leads to cost-up in the production and repair.
U.S. Pat. No. 4,946,295 which is incorporated in the present specification by reference, discloses another example of the bearing unit with rpm detector where the sensor is easily-engaged and disengaged with and from the bearing unit for easy inspection and repair. No special tool is used to install the sensor at the end of the stationary outer ring. However, no seal device is installed in this structure to protect the encoder and sensor from outside. Specifically, the seal ring 10 in this structure is used for isolating the space for installing the rolling members 3 from outside, but not for isolating the encoder and sensor from outside. Accordingly, for example, when it rained, water drops may be kept attached to the clearance between the encoder 19 and sensor 8, which may lead to damages of the encoder and/or sensor if the automobile is started with the attached water drops frozen.
JP Patent Publication TOKUKAI BEI No. 9-1964945 discloses another example of the bearing unit with rpm detector, where the holder 26 with the sensor 12a embedded therein can be easily installed and removed with respect to the cover 23 fixed to the outer ring 2a without any special tool. However, some improvements are required in assembling the bearing unit with rpm detector. Specifically the cylindrical support body 27 must be placed in alignment with the holder 26 in phase in a circumferential direction. Therefore, the holder must often be rotated inside the cylindrical support body, but due to the presence of the elastically compressed O-ring on the cylindrical support body, the force to rotate the holder is substantially large to easily worsen the assembly performance of the bearing unit with rpm detector. In addition to the assembly performance, the performance of the rotational speed sensor must be taken into consideration with respect to the installation of the holder into the cover of the bearing unit.
The mechanism of the rotational speed sensor is detailed later referring to FIGS. 73 to 76.